Background : The non-dipper is known to be related to worse prognosis in a population study. But the factors related to non-dipper are not so extensively evaluated in a clinical situation or high risk situation. This study is to characterize the subjects enrolled in Kor-ABP study and to define the factors related to non-dipper status. Methods : 1753 among 1916 subjects were analyzed. Exclusion criteria were incomplete data for sleep duration and excessive errors in nocturnal blood pressure(BP) resulting in incomplete nocturnal readings. Non-dipper was defined by nocturnal dipping less than 10%. Results : Age of the study subjects was 54.2 짹 14.9 years. Female was 49%. Daytime, noctrunal, and 24 hour ambulatory BPs were 135.7 짹 15.5 / 85.7 짹 11.8 mmHg, 126.8 짹 18.6 / 78.8 짹 13.3 mmHg, and 132.9 짹 15.6 / 83.1 짹 11.4 mmHg, respectively. Daytime heart rate was 73.4 짹 10.1 beats per minute. % dipping was 6.5 짹 8.7. Non-dipper was noted in 66.5 %. Positively correlated factors for nocturnal dipping were current drinking ( r = 0.060 , p = 0.011), smoking ( r = 0.083, p < 0.001 ), and sleep duration ( r = 0.073, p = 0.002). Negatively correlated factors for nocturnal dipping were age( r = -0.061, p = 0.009) and daytime measurement interval ( r = - 0.096, p < 0.001). Correlation coefficients for non-dipper were similar. Sleep quality and stroke history were 0.052 ( p = 0.028 ) and – 0.048 ( p = 0.039) only in simple Pearson correlation analysis. In multiple linear regression analysis, smoking ( 棺 = 0.061, p = 0.018), sleep quality (棺 = 0.059, p = 0.018 ), and daytime measurement interval (棺= - 0.109, p = 0.0001) were independent factors. In multiple logistic regression analysis, smoking ( OR: 0.704, p = 0.018) and daytime measurement interval ( OR : 1.03, p = 0.0001) were independent factors. Conclusion : Smoking and frequent daytime measurement interval overestimate nocturnal dipping and dipper. These findings should be considered in the analysis regarding nocturnal BP.